I think adding a concentrated spray on the sides of the glass when you do a water change(do a larger than normal) can hit it good.
You can still use the credit card, just not around those seam edges.

You can turkey baster the rest of the way down below the water level with a concentrated PO4 solution.

I'd add about 1 table spoon in 200 mls of water.

After the treatment, do a water change in a day.

Also, doing more water changes, cleanings etc more frequently and seeing what happens after is a good idea anytime you have an algae issue.
Green water cannot be beat that way, but most of the others can.

Excel really helps to resolve a CO2 issue.
I'm talking about the plant, not the algae there.

How's the surface current and tank mixing?
Tried CO2 misting?
What type of filter is this?

Regards,
Tom Barr